With improvement of computer performance and high development of multimedia technology, analogical images of words or patterns can be captured using an optical scanner, and then transformed into digital signals. As a result, after the process of transforming the analogical images into the digital signals, an image file can be showed, identified, edited, saved or output by a computer or other instruments.
In a scanning system, one of the critical factors affecting scanning qualities is whether an image of a scanned document can be accurately received by an optical sensor so that the optimum effect of receiving the image can be obtained under the optimum operation of the optical sensor. However, in general, it is possible that the effect of dispersion of light makes the image of a scanned document not accurately to be received by the optical sensor. Referring to FIG. 1 and FIG. 2, FIG. 1 is a schematic view showing the internal structure of a conventional scanning chassis; FIG. 2 is a top view schematically showing a conventional light transparent slot. A scanning chassis 100 mounted under a glass panel 190 is suited for scanning a document 180 put on the glass panel 190. The scanning chassis 100 can move in a right or left direction to scan the document 180. The scanning chassis 100 includes a case 110, a light source 120, three reflectors 130, a lens assembly 140, an optical sensor 150 and a printed circuit board 160. The light source 120 is mounted on a light carrier 118 of the case 110 and neighbors the glass panel 190. The reflector 130 and the lens assembly 140 are mounted inside the case 110. The optical sensor 150 is mounted on the printed circuit board 160 screwed on the case 110. The optical sensor 150 can be electrically connected with the printed circuit board 160. The case 110 has a light transparent slot 112 through which the image 124 of the document 190 can pass into the inside of the case 110. The light source 120 is, for example, a fluorescent lamp that can emanate light 122. The light 122 can illuminate the document 180 through the glass panel 190 and an image 124 can be generated at the place where the document 180 is illuminated by the light 122. Passing through the glass panel 190 and the light transparent slot 112, the image 124 can be projected on the reflector 130 and then the reflector 130 can reflect the image 124 in order that the image 124 can be projected on the lens assembly 140. Subsequently, the lens assembly 140 can refract the image 124 and then the refracted image 124 can be projected on the optical sensor 150.
As shown in FIG. 2, the conventional light transparent slot 112 shapes like a rectangle. In general, dispersion of light passes into the case 110 through the middle region of the light transparent slot 112 shaped like a rectangle with higher probability than through the two sides of the light transparent slot 112. That leads the tinge, sensed by the optical sensor, of the image of the document to be different because of different places where the document is put. Therefore, the quality of the image 124 can be lowered and noises can be increased.